For the purpose of simplifying the explanation, a smearing or spreading method of subject blood over a slide for microscopic observation (examination) used for medical diagnoses will be taken as an example. Obviously, subject matter other than blood may be spread according to the present invention.
As will later be described, referring to the drawings, conventionally known arts of smearing a subject blood over a slide are all disadvantageous or faulty in that the smears prepared are of non-uniform thickness according to the location and have a non-uniform distribution of cells.
As representative of the prior art, the Lecture on Clinical Examination Vol. 15, Haematology, by Shiro Hino published in 1972 from the ISHIYAKU SHUPPAN (Medical and Dental Pharmaceutics Publishing Co. Ltd.) will be partly cited, referring to pages 134-149. Besides, the following two books should be referred to as influential writings in this field: (1) Hematology for Medical Technologist, 3rd Edition, by SEIBERD, C. E., published by LEE AND FEBIGER in 1964, pages 219-251. (2) Clinical Hematology, 6th Edition, by WINTROBE, M. H., published by LEE AND FEBIGER in 1967, pages 444-447.
In one method, a technician holds a slide horizontally in one of his hands on which is placed a drop of subject blood, near one end of the slide, and a spreader slide (hereinafter simply called spreader) in the other hand so as to touch the first slide on the subject blood with the inner lower surface of the spreader at the lower end thereof selecting a certain acute angle within the range of 20-40 degrees. The drop of the subject blood positioned in a wedge-shaped space formed between the slide and the spreader contact both by capillary action, and spreads as a film over the slide surface as a film, as the spreader is moved horizontally at a certain constant speed, with the one end thereof being kept in touch with the slide surface and the contact angle kept unchanged.
Such a smear of blood is to be examined under a microscope, after fixing and staining, for providing necessary data for medical diagnoses based on, e.g., kind, type, or number of blood cells. The above-mentioned method of smear preparing is faulty for this purpose in that the thickness of the smear is largest in the spread-initiating portion and gradually decreases toward the spread terminating portion tapering like a wedge (See FIG. 3). The blood cells are deformed and become unsuited for dyeing in the former (thick) portion and are too scanty in distribution density in the latter (thin) portion, both of which are useless or valueless as data for the medical diagnoses. Such a tendency has heretofore limited the use of such smears, in microscopic examination as diagnostic data, only to the central portion thereof having a suitable thickness. In actuality, the distribution by type of blood cells in a smear is not uniform. Using only a portion of such a smear, wherein blood cells are locally or non-uniformly distributed, as a sample for microscopic examination is not good for medical diagnoses, being liable to lead to an erroneous judgement. It has, furthermore, become evident that such a non-uniformly distributed smear is unsuitable for examination employing an automatic cell discriminating instrument which is connected with an electronic computer. It often makes the examination itself unfeasible.
As a second known method, a mechanical spreading of subject blood employing a mechanical system in place of the above-mentioned manual spreading can be cited, in which the spreader is moved by a mechanical device, not by a human hand. This method has only changed the means of moving the spreader from manual to mechanical, leaving the spreading function itself utterly unchanged or unimproved. It is far from being free from the conventional disadvantages.
As a third method, a smear spreading by means of only centrifugal force, without depending on a spreader, has been developed. It also tends to render the distribution of blood cells non-uniform owing to the difference of specific gravity in various white corpuscles.